This proposal deals with the structure, translation and replication of potyviruses using tobacco etch virus as the model system. The potyviruses are the largest group of plant viruses affecting several important food, fiber and horticultural crops. The objective of this propsal is to study the molecular biology of these viruses, since we believe that the information gained would enhance our understanding of the basic principles underlying virus genome organization and replication. It is proposed to: (1) characterize the genome of TEV by sequencing, cloning and translational studies; (2) determine some of the similarities or disparities between the genome of different available potyviruses; (3) study the replication of the virus in the plant by analysis of virus-related subgenomic RNA and presence of virus-related proteins; (4) determine the nature of the translational products of the subgenomic RNA species; (5) characterize the nature of the virus-related inclusion body proteins. The p]otyviruses are similar to the animal picarnaviruses such as polio in having a poly(A) tail and genome-linked protein. However, there are important differences. Thus, for example, polio and other related viruses have a translational strategy involving the production of a single large polypeptide which is then processed. The potyviruses on the other hand, appear to have a different strategy involving the geneation of sub-genomic RNA species. The exact origin of these sub-genomic species and their function is not known. Further, the polyvirus replication strategy involves the production of specific types of inclusion bodies. Thus, although the potyviruses are somewhat structurally similar to the animal picarnaviruses with respect to the genome, their replicaton and translational strategies appear to be different. In view of these it is likely that a study of these viruses would lead us to some new concepts about the basic biology of viruses in general.